ok. I currently have 2 383 motors with 6" rods. One has H beam and Mech. roller cam, the other Eagle SIR Hydr. 106 LS cam. The H beams cleared the Roller cam no problem. The grinding on the block was no different then with a 5.7 rod. The Sir Rods hit the cam lobes on 2 cylinders. A quick grind on the back side of the rods and it was fixed. As far as block clearance... same on both. No disadvantage in block clearance. The pistons on both motors have a oil support ring that has to go on after the rods have been mated to the pistons. The set up seems to work just fine. Havent blown either motor up yet despite 7000 - 8000 rpm on the roller motor, and 6500 on the Hydraulic one. basically either way works just fine.